The objective of the invention is a method for conveying a load between location sites, preferably sub-methods for gripping the load, placing the load on a desired site and for controlling the crane based on information received from the identification means, as well as an equipment therefor.
A crane is used to lift and move rolls, containers or corresponding products from one place to another with at least one grip member, e.g. a C-hook, or with two grip members placed on the opposite sides of the load to be gripped, or with several grip members. Bridge cranes, hosting cranes, is knuckle boom cranes can be moved fairly precisely on rails, but several factors, such as wind, stretching of the crane cable, swings, bending of the crane construction caused by the weight of the load to be lifted, cause trouble in gripping the load and moving it to a desired site. Piling of the load causes trouble when the first goods are placed at the bottom of the load, or when stacking the outer portions of the pile, when there is not corresponding goods on the other side of the goods to be stacked but an edge, e.g. the edge of a ship hold or a floor (empty). This has been a problem due to the lack of a suitable observation means for this purpose to survey the desired site to obtain an image of the correct angle. All machines, ships, trains, trucks and movable goods can temporarily be positioned in relation to each other either by measuring electrically or also physically by a metering device. A known satellite positioning is the GSP-method (Global Positioning System), in which the positioning of the gripper or the machine part in relation to the positioning satellites is implemented with an accuracy of 0.1-1 meter. The GSP-positioning functions so far only outdoors. This is not always functional or sufficiently accurate.
When loads are being conveyed on crane cables, the load comes into a swinging movement, which makes the work difficult. The swings have been taken into consideration by using e.g. a synchronizer, whereby each produced change of acceleration is followed by another equally big change but in the opposite direction after a certain time period. To damp the swing, an optimal speed profile is calculated for the motion, which eliminates the swing at the end of the motion and minimizes the time used for the motion. Previously known solutions have thus defined the swing equation of the load based on calculated values. The swing of the load can be controlled by the information. The swing control is in fact based on the calculated default formula. No real time control is arranged. When current systems use different counterforces to absorb the load swing, the target site might drift elsewhere than to a certain site, and a repetition of the same stop event at the same known target site seems fairly theoretical.
The swing absorption of the load should also function with a gantry robot lifting pillar or other structure preventing the free swinging of the load and the gripper. The robot lifting pillar is assumed to be rigid with a small load. When the bulk to be transferred is increased, bending is conducted also on the pillar by the load carrying structures, but these do not follow the mathematical harmonic swing formula, because the load carrying structures of the load act as springs. The arranging of the swing absorption by some mathematical formula would thus require empirical tests, as the spring constants etc. of the structures vary in e.g. a bridge construction according to how close the trolley is from the end carriers of the bridge. The above presented situations can also be managed by the invention.
The problem can e.g. be that when the crane driver obtains information about the transit distance of the cable, this does not generally enable him to drive the load sufficiently accurate to the desired site, as e.g. the 10 ton and 30 ton load carried by the crane causes a bending of a different size on the crane bridge and also on the stretching of the cable. Changes in the loading platform of the goods (ship's draft) can also cause problems to the crane driver. One solution to the above mentioned problems has been to e.g. identify lines marked in the ground or alike by a recognition means provided in the crane, based on which the load is transferred and the location becomes known. This is characteristic for container travelling gantry cranes. The markings cause additional work and the maintenance can be difficult.